The present invention relates to the sampling of fluid in a fluid reservoir. More specifically, the present invention concerns devices and methods for sampling fluid remotely and with minimal disturbance of the fluid.
It is often desirable to remotely withdraw fluid samples from a reservoir, while minimizing the disturbance of the fluid in the reservoir during sampling. For example, such sampling is desirable when a fluid sample is taken from the reservoir of a high voltage, high amperage switch in an electrical power distribution system.
Insulating liquid (which is usually a petroleum-based oil) is often provided in a high voltage, high amperage electrical switch to extinguish the electrical arc which is otherwise produced when the switch is de-energized. The insulating quality of the liquid in these switches has a direct bearing on their reliability and operation. The liquid can lose insulating quality through contamination with non-insulating material, frequency of use, or the mere passage of time. In particular, the insulating quality of the liquid can be reduced when metal components or gaskets in the switch corrode thereby allowing metal particles and/or water to get into the liquid.
Failing to replace degraded insulating liquid in an electrical switch, or to replace the entire switch, can result in switch failure. In a utility power distribution system, a switch failure can in turn cause substantial system maintenance costs, lost revenues, and dissatisfied utility customers. Therefore, the liquid in these electrical switches should be periodically checked to determine whether the insulating liquid or the switch ought to be replaced.
The conventional way of checking the quality of the insulating liquid is to first de-energize the switch. Next, a plug from the reservoir containing the insulating liquid is removed and a sample of the insulating liquid is taken. The sample is then tested for its insulating characteristics.
The foregoing procedure has substantial drawbacks because, before the switch can be de-energized, it must be isolated within the electric power system to avoid interrupting service. Power system switch isolation requires complex and expensive measures, including substantial manpower. As a result, sampling of the insulating liquid in such switches is infrequent. The switches are generally sampled only when visual inspection reveals evidence of potential breakdown of insulating liquid, such as corrosion on the outside surfaces of a switch. However, breakdown of the insulating liquid can occur without such external evidence of corrosion. Consequently, more switch failures take place than would otherwise occur if the insulating liquid could be tested without de-energizing the switch.
There is therefore a need for a device and method for remotely sampling insulating fluid in an electrical switch without de-energizing the switch. Stated another way, there is a need for a device and method for remotely removing a plug on a fluid reservoir of an electrical switch and for remotely sampling the fluid without substantially disturbing the fluid.